1. Field of the Invention
This invention relates to a disk-shaped recording medium, such as, a magneto-optical disk, and an apparatus for recording and/or reproducing data on such recording medium. More particularly, the invention relates to a disk-shaped recording medium on which servo signals are recorded by discrete preformatting and to an apparatus in which a sampled servo technique is utilized for recording and/or reproducing data on the disk-shaped recording medium.
2. Description Of The Prior Art
There has recently been developed and marketed disk-shaped recording media with which optical or magneto-optical signal recording and/or reproducing methods are employed. Examples of known types of disk-shaped recording media include a read-only memory (ROM) type recording medium, such as, a compact disk (CD), a write-once type recording medium on which data can be written only once by the user, and a recording medium on which data can be rewritten, that is, overwritten, such as, a magneto-optical disk. As one of the techniques for realizing a unified recording format for these various recording media, it has been proposed to use a so-called sampled servo technique in which, in a manner similar to that used in the so-called sector servo in the case of hard magnetic disks, servo signals are pre-formatted at intervals of a predetermined distance or angle on concentric circular tracks or on successive tracks forming turns of a spiral, and such discrete servo signals are sampled and held during disk driving to perform continuous servo control.
This type of disk-shaped recording medium has been proposed, for example, as disclosed in the co-pending U.S. Pat. Application Ser. No. 07/348,486, filed on Apr. 18, 1989, now U.S. Pat. No. 4,925,717 and having a common assignee herewith, in the form of an optical disk d having the recording format shown in FIG. 1. The optical disk is shown to include an annular label section 2 extending around a center aperture 1 and an annular recording surface 3 surrounding the label section 2. On this recording surface 3, there are provided recording tracks tk which are concentric with the center aperture 1, or which are constituted by successive turns of a continuous spiral centered at the aperture 1. Each of the tracks tk is divided into a predetermined number of sectors SC.sub.1 to SC.sub.m. A plurality of sectors bearing the same suffix numerals in the several tracks tk, such as the sectors SC.sub.1, are arranged in radial alignment with each other on the optical disk d. Each of the sectors SC.sub.1 to SC.sub.m of each of the tracks includes a predetermined number n of blocks BL.sub.1 to BL.sub.n, arranged along the respective track tk, with the incipient block BL.sub.1 of each sector being an address data division AD. In respect to these blocks BL.sub.1 to BL.sub.n, it will be seen that a plurality of blocks bearing the same suffix number, such as, the blocks BL.sub.1 of the sectors SC.sub.1 to SC.sub.m, respectively, are arranged in radial alignment with correspondingly identified blocks BL.sub.1, in the other tracks on the optical disk d. Each of the blocks BL.sub.1 to BL.sub.n in each of these sectors SC.sub.1 to SC.sub.m has a control record region AR.sub.c at its leading or incipient side, followed by a data write region AR.sub.D.
The control record region AR.sub.c of each of the blocks BL.sub.1 to BL.sub.n is divided into a servo region AR.sub.s and a traverse region AR.sub.T. In the servo region AR.sub.s, a pair of tracking data pits Q.sub.A and Q.sub.c are arrayed so as to be offset, at opposite sides, in respect to a track centerline K.sub.c and are spaced, at a predetermined interval, for example, an interval of eight channel bits, along the track direction. A clock data pit Q.sub.B is arranged between these track data pits Q.sub.A and Q.sub.C and is located on the track centerline K.sub.C. In the traverse region AR.sub.T, a pair of traverse data pits Q.sub.D and Q.sub.E are arrayed at a distance P from each other, and such distance P is allotted for each recording track tk with the clock data pit Q.sub.B as the reference.
Each control record region AR.sub.C has a data recording capacity of 30 channel bits. Among these 30 channel bits, the 7th and the 15th channel bits are allotted as the recording positions of the tracking data pits Q.sub.A and Q.sub.C, the 11th channel bit is allotted as the recording position for the clock data pit Q.sub.B and the 19th to 27th channel bits are allotted as the recording area for the traverse data pits Q.sub.D and Q.sub.E.
In an optical disk recording and/or reproducing apparatus employing the above described optical disk d as the disk-shaped recording medium therefor, channel clocks may be reproduced from the clock data pits Q.sub.B while tracking control is effected on the basis of the tracking data pits Q.sub.A and Q.sub.C provided in the servo region AR.sub.S of the control record region AR.sub.C of each of the blocks BL.sub.1 to BL.sub.n preformatted on the optical disk d. On the other hand, the pit pattern of the traverse data pits Q.sub.D and Q.sub.E may be read from the traverse region AR.sub.T on the basis of the playback clocks to perform traverse counting of the recording tracks on a track-by-track basis.
However, the above described optical disk d is disadvantageous in that, since the traverse region AR.sub.1 and the servo region AR.sub.S are provided in the trailing half and the leading half, respectively, of the control record region AR.sub.C, it is necessary to read the tracking data pits Q.sub.A and Q.sub.C of the servo region AR.sub.S and the clock data pits Q.sub.B, in the vicinity of the points at which switching occurs from the writing scanning for the data write region AR.sub.D to the read-out scanning for the control record region AR.sub.C in the course of a recording operation during which the data write scanning for the data write region AR.sub.D and the servo data read-out scanning for the control record region AR.sub.C are repeated alternately, so that stable servo controlling cannot be achieved.